Electric machine systems

ABSTRACT

An electric machine system disclosed herein comprises first and second electric machines configured to drive a load. The first electric machine has a plurality of first rotors. The second electric machine has a plurality of second rotors. At least one of the second rotors is indexed relative to a respective one of the first rotors to, in use, provide a torque phase offset between the first and second electric machines. A shaft is coupled to the load and connects the respective one of the first rotors with the at least one of the second rotors. The respective one of the first rotors is coaxial with and axially spaced apart from the at least one of the second rotors.

FIELD

This relates generally to electric machines, and more particularly tomulti-rotor electric machines such as motors and generators.

BACKGROUND

Electric machines with multiple rotors are known and may provideenhanced power over conventional electric machines. However, knownmultiple-rotor electric machines may provide unsteady output torquecharacteristics on individual rotors, and may require complexconfigurations. Moreover, multiple-rotor electric machines may have lowdurability due to variability in torque at the rotor level duringoperation. Improvement is desirable.

SUMMARY

In one aspect, the disclosure describes an electric machine systemcomprising:

a first electric machine configured to drive a load, the first electricmachine having a plurality of first rotors;

a second electric machine having a plurality of second rotors, at leastone of the second rotors indexed relative to a respective one of thefirst rotors to, in use, provide a torque phase offset between the firstand second electric machines; and

a shaft coupled to the load, the shaft connecting the respective one ofthe first rotors with the at least one of the second rotors, therespective one of the first rotors being coaxial with and axially spacedapart from the at least one of the second rotors.

The electric machine system may comprise a third electric machine havinga plurality of third rotors, at least one of the third rotors indexedrelative to the respective one of the first rotors and the at least oneof the second rotors to, in use, provide a torque phase offset betweenthe first and third electric machines and a torque phase offset betweenthe second and third electric machines, wherein the at least one of thethird rotors is connected to the shaft.

The torque phase offset between the first electric machine and thesecond electric machine may be 120 degrees.

The torque phase offset between the second electric machine and thethird electric machine may be 120 degrees.

A respective one of the rotors in the pluralities of first, second andthird rotors may be disposed at different axial positions relative tothe shaft.

A respective one of the rotors in the pluralities of first, second andthird rotors may be coaxial.

The shaft may be drivingly coupled to the load via one or more gears.

A respective one of the rotors in the pluralities of first and secondrotors may be disposed at different axial positions relative to theshaft.

The electric machine system may comprise a plurality of shaftsrespectively interconnecting a respective one of the plurality of firstrotors with a respective one of the plurality of second rotors.

Adjacent first rotors may be indexed to have a positional phase offsetof 180 degrees with each other.

Adjacent second rotors may be indexed to have a positional phase offsetof 180 degrees with each other.

The plurality of shafts may be drivingly coupled to the load viarespective gears.

Each of the plurality of shafts may have parallel rotation axes.

The first rotors may be disposed to define a first circular arrayarrangement. The second rotors may be disposed to define a secondcircular array arrangement. The first circular array arrangement offirst rotors may be coaxial with the second circular array arrangementof second rotors. The first circular array arrangement of first rotorsmay be axially offset from the second circular array arrangement ofsecond rotors.

Embodiments can include combinations of the above features.

In another aspect, the disclosure describes an electric machine systemcomprising:

a first electric machine configured to drive a load, the first electricmachine having a plurality of first rotors driven using electric powerhaving a first phase;

a second electric machine configured to drive the load, the secondelectric machine having a plurality of second rotors driven usingelectric power having a second phase, the second phase different fromthe first phase; and

one or more shafts, each shaft connecting a first rotor with a secondrotor, the first rotor being coaxial with and axially spaced apart fromthe second rotor.

The electric machine system may comprise: a third electric machinehaving a plurality of third rotors driven using electric power having athird phase, the third phase different from the first phase and from thesecond phase, wherein each shaft connects one of the third rotors withthe one of the second rotors and the one of the first rotors.

Each of the one more shafts may be drivingly coupled to the load by oneor more gears.

The first rotors may be indexed to have a positional phase offsetrelative to each other.

The first phase and the second phase may be offset by 120 degrees.

The second electric machine may be axially offset from the firstelectric machine.

The first electric machine may have a first common stator and one ormore first windings circumferentially spaced apart on the first commonstator. The second electric machine may have a second common stator andone or more second windings circumferentially spaced apart on the secondcommon stator. The one or more second windings may be circumferentiallyoffset from the one or more first windings.

The one or more shafts may be drivingly coupled to the load viarespective gears.

The one or more shafts may have parallel rotation axes.

The first rotors may be disposed to define a first circular arrayarrangement. The second rotors may be disposed to define a secondcircular array arrangement. The first circular array arrangement offirst rotors may be coaxial with the second circular array arrangementof second rotors. The first circular array arrangement of first rotorsmay be axially offset from the second circular array arrangement ofsecond rotors.

Embodiments can include combinations of the above features.

In another aspect, the disclosure describes an electric machine systemcomprising:

a first electric machine rotor;

a first gear connected to the first electric machine rotor and to afirst input/output shaft; and

a second gear connected to the first electric machine rotor and to asecond input/output shaft, the first electric machine rotor disposedbetween the first gear and the second gear.

A radius or number of teeth of the first gear may be different from aradius or number of teeth of the second gear.

Each of the one or more shafts may include a second electric machinerotor disposed between the first gear and the second gear.

Each of the one or more shafts may include at least a third electricmachine rotor disposed between the first gear and the second gear.

The electric machine rotors of each of the one or more shafts may beindexed to have a positional phase offset relative to each other.

The electric machine rotors of each of the one or more shafts may beindexed to provide a torque phase offset relative to each other whenoperating in a motoring mode.

The electric machine rotors may be operable in a generating mode and ina motoring mode.

The one or more shafts may have parallel rotation axes.

The one or more shafts may be disposed to define a circular arrayarrangement.

Embodiments can include combinations of the above features.

In another aspect, the disclosure describes a power transmission systemcomprising:

an input shaft;

an output shaft;

one or more electric machine rotors;

a first gear connected to the input shaft; and

a second gear connected to the output shaft, the one or more electricmachine rotors being disposed between the first gear and the secondgear.

A radius or number of teeth of the first gear may be different from aradius or number of teeth of the second gear.

Each of the one or more rotor shafts may include a second electricmachine rotor disposed between the first gear and the second gear.

Each of the one or more rotor shafts may include at least a thirdelectric machine rotor disposed between the first gear and the secondgear.

The electric machine rotors of each of the one or more rotor shafts maybe indexed to have a positional phase offset relative to each other.

The electric machine rotors of each of the one or more rotor shafts maybe indexed to provide a torque phase offset relative to each other whenoperating in a motoring mode.

The electric machine rotors may be operable in a generating mode and ina motoring mode.

The one or more rotor shafts may have parallel rotation axes.

The one or more rotor shafts may include a plurality of rotor shaftsdisposed to define a circular array arrangement.

Embodiments can include combinations of the above features.

Other features will become apparent from the drawings in conjunctionwith the following description.

BRIEF DESCRIPTION OF DRAWINGS

In the figures which illustrate example embodiments,

FIG. 1 is a schematic perspective view of portions of an exampleembodiment of an electric machine having multiple rotors;

FIG. 2 is a schematic front cut-away view of portions of the electricmachine of FIG. 1;

FIG. 3 is a schematic partial cut-away view of a portion of the electricmachine of FIG. 1;

FIG. 4 is a simplified schematic perspective view of portions of anexample embodiment of an electric machine with multiple rotors on acommon shaft;

FIG. 5 is a diagram depicting the torque delivered by a rotor shaft ofan electric multi-rotor machine;

FIG. 6 is a diagram depicting the torque delivered by a rotor shaft ofan electric machine with multiple rotors on a common shaft;

FIG. 7 is a simplified front cut-away view of portions of the machinedepicted in FIG. 2;

FIG. 8 is a simplified front cut-away view of an electric machine havingmultiple rotors;

FIG. 9 is a side view of an electric machine system having multipleelectric machines with multiple rotors in parallel;

FIG. 10A is a simplified schematic side cross-sectional view of anindividual rotor shaft of the machine system of FIG. 9;

FIG. 10B is a view of a rotor on axis A-A in FIG. 10A;

FIG. 10C is a view of a rotor on axis B-B in FIG. 10A;

FIG. 10D is a view of a rotor on axis C-C in FIG. 10A;

FIG. 11 depicts an alternative configuration of an electric machinesystem having multiple electric machines with multiple rotors inparallel;

FIG. 12 is a partial cross-sectional view of an electric machine systemhaving multiple electric machines with multiple rotors and multiplegears per rotor shaft; and

FIG. 13 is a schematic partial cross-sectional view of an electricmachine system having independent input and output shafts.

DETAILED DESCRIPTION

The disclosure provides electric machines, and in particular improvedmultiple-rotor electric machines such as motors and generators. In someembodiments, the machines described herein can provide improvedoperational characteristics and durability. In various aspects, forexample, the disclosure provides electric motors and generators having aplurality of magnetized rotors, which may include or be in the form ofsingle bi-pole magnets (i.e., two-pole rotors). The rotors areconfigured to drive and/or be driven by a common shaft, for example bysuitable combinations and configurations of gears.

In some embodiments, the rotors are magnetically indexed, in pairs, withrespect to each other and to corresponding electrical windings suchthat, when a current is passed through the one or more windings, therotors provide phased rotary power to the common shaft. Alternatively,when torque is applied to the common shaft or gears connected thereto, aphased electrical output may be provided to the windings.

In some embodiments, the rotors are magnetically indexed along differentplanes perpendicular to the axial direction of the common shaft, andconnected by common rotor shafts. That is, all of the rotors in a firstplane may share a common phase, and all of the rotors in a second planemay share a common phase which is offset from the phase of the firstplane. In some embodiments, there may be 3 planes each offset by 120degrees. Any suitable number of planes may be used with suitableoffsets.

Various aspects of preferred embodiments of electric machines accordingto the disclosure are described herein with reference to the drawings.

Electric machines may have more than one rotor. An example of amulti-rotor electric machine is provided in U.S. Pat. No. 8,232,700 B2,the contents of which are hereby incorporated by reference in theirentirety.

FIG. 1 is a schematic perspective view of portions of an embodiment ofan electric machine 100 having multiple rotors (also referred to hereinas a “multi-rotor electric machine”). As illustrated, machine 100comprises magnetic rotors 102, windings 108, stators 122, and shaft 104.In the embodiment shown, machine 100 comprises a plurality of magneticrotors 102, each configured to rotate about an independent rotor shaft116. Each rotor shaft 116 is configured to, under the impetus ofmagnetic rotors 102, drive shaft 104 via gears 118 and central gear 120when machine 100 is operated as a motor and an electric current isapplied to windings 108. Alternatively, magnetic rotors 102 areconfigured to rotate, and thus cause the flow of electric current inwindings 108, when a torque is applied to shaft 104, such that machine100 acts as a generator. It should be appreciated that gears 118 areshown without teeth in FIGS. 2 and 3 for the sake of clarity. Gears 118may be provided in any suitable form, including, for example, toothlesswheels engaged by friction.

In the embodiment shown, each rotor shaft is supported by front and backplates with suitable bearings (not shown), and is formed integral withor otherwise connected to a drive gear 118, which is configured toengage a central gear 120. In some embodiments, central gear 120 isformed integral with or otherwise connected to shaft 104, such thatrotation of one or more rotors 102 causes drive gears 118 to drivecentral gear 120, and therefore shaft 104, into rotation.

In some embodiments, rotors 102 are configured to operate inelectromagnetically independent pairs. That is, rotors 102 a, 102 b canbe grouped magnetically into independent pairs 160, such that there isno provision of magnetic material linking any two pairs 160 a, 160 b ofrotors together, and the links between separate rotor pairs 160 are thegears 118 or other mechanical couplings between them, and possibly ashared electric phase. The rotors 102 a, 102 b in a given pair 160 canbenefit from the provision of common magnetic circuit components, suchas stators 122 and/or windings 108. Such a configuration can reduce theamount of magnetic material required for operation of the rotors, withcorresponding cost and weight savings.

In the embodiment shown in FIG. 3, each rotor 102 comprises one or moremagnets mounted on a rotor shaft 116 and retained, particularly whenrotating, by containment sheath 126. Magnets 128 comprise north andsouth poles (denoted “N” and “S” respectively in the figures). In someembodiments, rotors 102 are bi-pole rotors. In some embodiments, rotors102 a, 102 b in a given pair are indexed such that magnets 128 aremounted, and rotate, (a) as individual rotors 102, in a desired phasewith respect to their pair mates 102 a, 102 b, and (b) by pairs 160, ina desired paired phase with respect to other pairs 160 and winding(s)108. Advantages associated with this configuration are explained in U.S.Pat. No. 8,232,700, the contents of which are incorporated by reference.

Windings 108 may be provided in any configuration suitable for use inaccomplishing the purposes described herein. For example, single Litzwire or multiple strand windings 108 may be used in configuring eithermachine 100, individual rotors 102, rotors pairs 160, or other desiredsets of rotors 102. The use of multiple windings 108 in a machine 100can be used, as for example in conjunction with suitable mechanicalindexing of the rotors 102 to fully or partially provide desiredphasings in torque applied by rotors 102 to shaft or load 104. Forexample, 3-phase windings used in known electric machines may be formedby appropriate interconnections of the separate windings in machines 100according to the present disclosure.

As depicted, each rotor-driven gear 118 engages the periphery of centralgear 120 such that total torque applied to central gear 120 is the sumof the torques applied by the gears 118. If winding(s) 108 areconfigured substantially circumferentially about axis 200 of shaft 104and therefore machine 100, an index angle 112 may be defined betweenequators (that is, the line dividing magnet 128 into north and southhalves) 202 of individual magnets 128 and radii 204 extending from axis200 to the corresponding rotor 102. By suitable arrangement of rotors102 and/or gears 118, index angles 112 may be set at desired values forindividual rotors, and sets thereof, with the result that phased torqueoutput applied by each of the rotor pairs 160 can be applied to providesmooth, continuous torque to shaft 104, when operated as a motor. Whenoperated as a generator, smooth and continuous current may be outputfrom overall winding(s) 108.

FIG. 1 depicts an embodiment having 12 rotors 102 (or 6 pairs 160) and 6phases. As will be understood, embodiments described herein can beadapted to 6-rotor, 3-phase systems, 24-rotor, 12-phase systems, andother combinations.

In some embodiments, each rotor 102 a in a given pair 160 a may bephased magnetically at 180 degrees with respect to its pair mate 102 b.Further, each of the 6 pairs 160 a, 160 b, 160 c, 160 d, 160 e, 160 fmay be phased at 60 degrees relative to adjacent pairs. It should beappreciated that in FIG. 2, for simplicity, reference numerals 160 a-frefer only to respective pairs of rotors 102 a, 102 b.

Likewise, in a 6-rotor, 3-phase system, each adjacent rotor pair 160 a,160 b, 160 c can be indexed by 120 degrees with respect to adjacentpairs. The same logic may be applied to configurations with more orfewer rotors.

However, in spite of providing smooth and continuous torque to centralgear 120 as an overall system, each gear 118 in machine 100 suffers froma relatively high torque ripple (i.e., torques variations of a higheramplitude) during operation. That is, owing the nature of the operationof AC machines, the torque delivered by each rotor 102 varies from 0 tothe maximum output torque twice per cycle. The impact of this torqueripple may be substantial in terms of the working life for a gear, asthe gears are subjected to a wide variation of stress. The machine 100may require low-backlash gears and/or high strength gears, which areexpensive and may nevertheless be subjected to fretting damage over thecourse of operation.

FIG. 4 is a simplified schematic perspective view of portions of anexample embodiment of an electric machine system 400 having multiplerotors on a common shaft. As depicted, machine system 400 includes aplurality of multi-rotor machines 410, 410′,410″ located in differentplanes along the axial direction of shaft 104. In some embodiments, aswith machine 100, the rotors depicted in FIG. 4 are magnetically indexedin pairs 160 of rotors 102 a, 102 b which share a common stator 122. Insome embodiments, rotors 102 a and 102 b may be offset by 180 degrees.As depicted, in each machine in system 400, each rotor pair 160 a, 160b, 160 c, 160 d, 160 e, 160 f may have a phase offset of 60 degreesrelative to adjacent rotor pairs of the same machine. As depicted, therotors 102 of machine 410 are disposed to define a circular arrayarrangement about axis 200, and the rotors 102′ of machine 410′ aredisposed to define a circular array arrangement about axis 200 which isaxially offset from the circular array arrangement of machine 410. Insome embodiments, the circular array arrangement of machine 410 may becoaxial with the circular array arrangement of machine 410′.

In an example embodiment using 3-phase power, in first machine 410,windings for rotor pairs 160 a, 160 d may be supplied with current froma first phase (denoted as phase C). Windings for rotor pairs 160 b, 160e may be supplied with current from a second phase (denoted as phase A).Windings for rotor pairs 160 c, 160 f may be supplied with current froma third phase (denoted as phase B).

In the example embodiment of FIG. 4, windings for each pair 160 a′, 160b′, 160 c′, 160 d′, 160 e′, 160 f′ of rotors 102 a′, 102 b′ in secondmachine 410′ are similarly supplied by one of 3 phases (phase A, phaseB, or phase C). Relative to axis 200, the current for the windings insecond machine 410′ are phase shifted by 120 degrees. As such, windingsfor pairs 160 a′ and 160 d′ are supplied by phase A, windings for pairs160 b′ and 160 e′ are supplied by phase B, and windings for pairs 160 c′and 160 f′ are supplied by phase C.

Similarly, the current for the windings in third machine 410″ is phaseshifted by 240 degrees relative to first machine 410. As such, windingsfor pairs 160 a″, 160 d″ are supplied by B, windings for pairs 160 b″,160 e″ are supplied by phase C, and windings for pairs 160 c″, 160 f″are supplied by phase A.

As depicted, machine 400 includes one or more extended rotor shafts 416a which interconnect a given rotor 102 a in first machine 410 to acorresponding rotor 102 a′ in second machine 410′ and a correspondingrotor 102 a″ in third machine 410″. In some embodiments, shaft 416 ainterconnects a first rotor 102 a and a second rotor 102 a′ withoutinterconnecting a third rotor 102 a″. As depicted, the rotors 102 a, 102a′, 102 a″ are disposed at different axial positions relative to axis200 of shaft 104. In some embodiments, rotors 102 a, 102 a′, 102 a″ arecoaxial.

The total net torque delivered by rotor shaft 416 a can be the sum ofthe torque provided by rotors 102 a, 102 a′, 102 a″. Moreover, it willbe appreciated that each of rotors 102 a, 102 a′, 102 a″ is coupled toone of phase A, phase B, and phase C, respectively. As such, theresulting net torque provided to shaft 416 a would be the sum of torquesprovided by rotors which are coupled to phases A, B and C, which areeach offset by 120 degrees relative to the other phases. As such, theripple in torque delivered by rotor shaft 416 a may be substantiallyreduced. FIG. 5 is a diagram depicting the torque delivered by a rotorshaft 116 of machine 100. FIG. 6 is a diagram depicting the torquedelivered by rotor shaft 416 a of machine system 400. As will beappreciated, the torque delivered by rotor shaft 416 a exhibitssubstantially less torque ripple (i.e., torques variations of a loweramplitude) than machine 100.

Rotor shaft 416 b rotatably connects rotor 102 b in first machine 410 torotor 102 b′ in second machine 410′ and to rotor 102 b″ in third machine410″ to define collective rotor 450 b. Again, rotor shaft 416 b isprovided with torque from 3 rotors which are coupled to three separatephases A, B and C. As such, the torque delivered by collective rotor 450b exhibits substantially less torque ripple than machine 100. In someembodiments, rotors 102 a, 102 b in machine 410 are mechanically 180degrees out of phase, rotors 102 a′, 102 b′ in machine 410′ aremechanically 180 degrees out of phase, and rotors 102 a″, 102 b″ inmachine 410″ are mechanically 180 degrees out of phase with one another.This may further enhance the efficiency of machine system 400.

It should be appreciated that for simplicity, only two extended rotorshafts 416 a, 416 b are illustrated in FIG. 4. In some embodiments theremay be a corresponding extended rotor shaft 416 for each rotor in firstmachine 410, provided there is a corresponding rotor in at least asecond machine 410′ to which the extended rotor shaft 416 can beconnected. In some embodiments, the number of extended rotor shafts 416may be less than the number of rotors in a given plane. In someembodiments, the extended rotor shafts 416 may have parallel rotationalaxes.

Although FIG. 4 depicts an electric machine system 400 with 3 parallelmachines 410, 410′, 410″, it will be appreciated that embodiments withmore than 3 or fewer than 3 parallel machines 410 are also contemplated.Similar configurations can be implemented using the appropriate phasedifferences between magnetic cores in different planes. In embodimentswith two machines 410, 410′, the first rotor 102 a, second rotor 102 a′and shaft 416 a are coupled for common rotation.

In some embodiments, each rotor shaft 416 has a gear 118 affixed orconnected thereto. As depicted, gear 118 is affixed or otherwiseattached to rotor shaft 416 such that rotation of rotor shaft 416 causesgear 118 to rotate along the same rotational axis as the rotor shaft416. Gear 118 is configured to engage with central gear 120 to drive aload. Given that the torque ripple is substantially reduced for eachgear 118 owing to the rotor shaft 416 shared across machines 410, 410′,410″, it will be appreciated that some embodiments disclosed herein mayreduce the amplitude of the cyclic stress experienced by gears 118 whileengaging with central gear 120. This may in turn increase the workinglife of gears, and may allow for the use of less expensive materials forgears 118. The reduction in the likelihood that gears 118 will sufferdamage during operation may further increase the reliability anddependability of machine 400 relative to known electric machines.

FIG. 7 is a simplified front cut-away view of the machine 100 depictedin FIG. 2. As depicted, a common stator 122 is provided for each pair160 of rotors 102 a, 102 b. Each stator 122 has a winding 108, althoughit will be appreciated that in some embodiments, a stator has more thanone winding 108. In addition, windings for pairs 160 a and 160 d receivecurrent from phase A, windings for pairs 160 b and 160 e receive currentfrom phase B, and windings for pairs 160 c and 160 f receive currentfrom phase C. It should be appreciated that any two stators can beconnected by a single phase. In some embodiments, phase B is offset by120 degrees from phase A, and phase C is offset by 240 degrees fromphase A. The machine 100 may suffer from considerable losses duringoperation, and uses substantial quantities of iron, which impliesgreater weight and cost. Moreover, the configuration depicted in FIG. 7may require a number of rotors which is divisible by 3. Since the rotors102 a, 102 b are provided in pairs, this may limit the possibleconfigurations to those which include 6 rotors, 12 rotors, 18 rotors, orthe like.

It may be desirable to have greater flexibility in the number of rotorswhich can be included in a multi-rotor electric machine. Moreover, itmay be desirable to reduce the quantity of iron required for stators andtherefore the weight, cost, and losses associated with machine 100.

FIG. 8 is a simplified front cut-away view of an electric machine system800. As depicted, machine 800 includes a first multi-rotor machine 810located in a first plane. Machine 810 includes one stator 822 and aplurality of windings 808 (depicted as winding 808 ab for the windingappearing between rotors 802 a and 802 b, and so forth) and rotors 802a, 802 b, 802 c, 802 d, . . . , 802 n. It should be appreciated thatmachine 810 can have any number of rotors 802. That is, the number ofrotors 802 need not be in multiples of 3, and the rotors need not beindexed in magnetically independent pairs as with machine 100, so thereneed not be an even number of rotors 802. In some embodiments, there isone common stator 822 for all rotors 802 a, 802 b, 802 c, 802 d, . . . ,802 n in machine 810, and the electric power is supplied by a singlephase (e.g. phase A). In some embodiments, the electric power issupplied in the form of AC electric power and the machine 810 operatesas an asynchronous machine. In some embodiments, the electric power maybe supplied as DC current, and machine 810 may operate as a DC motor.

In some embodiments, rotors 802 a, 802 b, 802 c, 802 d, . . . , 802 nare disposed in a circular array arrangement circumferentially aroundaxis 200 of central shaft 104. An index angle may be defined betweenequators (i.e. the line dividing north and south poles) for individualmagnets for each rotor 802 and radii 904 extending from axis 200 to thecorresponding rotor 802. For simplicity, only radii 904 c, 904 d aredepicted for corresponding rotors 802 c, 802 d and index angles forother rotors 802 are omitted. As depicted, rotors 802 c and 802 d haveindex angles of 0 degrees, because the equator is parallel to radii 904c, 904 d, respectively. By suitable positional phase offset of rotors802 and/or rotor gears 818, index angles may be set at desired valuesfor individual rotors, with the result that torque output applied byeach rotor 802 can be enhanced.

The configuration of machine 810 in FIG. 8 may substantially reduce theamount of iron (e.g. for laminations) required, which may in turn reducethe weight, associated costs, and losses inside machine 810 duringoperation. In some embodiments, the configuration depicted in FIG. 8 mayrequire 40% less iron to produce similar output power relative tomachine 100. It will be appreciated that during operation, the outputtorque of each rotor 802 in machine 810 may exhibit a large degree oftorque ripple, as each rotor 802 a, 802 b, . . . 802 n varies betweendelivering no torque and the maximum output torque.

FIG. 9 is a side view of electric machine system 800 illustratingmultiple machines 810, 810′, 810″ in parallel on different planes. Asdepicted, machine 800 includes first machine 810 in a first plane,second machine 810′ in a second plane, and third machine 810″ in a thirdplane. The machines 810, 810′, 810″ are positioned substantiallyperpendicularly to axis 200 of shaft 104. In some embodiments, machines810, 810′, 810″ are substantially parallel to one another. In someembodiments, the circular array arrangement of rotors of machine 810 maybe coaxial with the circular array arrangement of rotors of machine810′. In some embodiments, the circular array arrangement of rotors ofmachine 810 may be axially offset from the second array arrangement ofrotors of machine 810′.

Rotor shafts 816 (e.g. rotor shaft 816 d) interconnect a respectiverotor in machine 810 (e.g. rotor 802 d) to a respective rotor in machine810′ (e.g. rotor 802 d′) and to a respective rotor in machine 810″ (e.g.rotor 802 d″). As depicted, respective gears 818 are connected oraffixed to rotor shafts 816. As depicted, gear 818 is affixed orotherwise attached to rotor shaft 816 in a manner such that rotation ofrotor shaft 816 causes gear 818 to rotate in the same direction and witha common rotational axis to shaft 816. In some embodiments, rotor shaft816 d is drivingly coupled to shaft 104 or a load via gear 818 d. Asreferenced herein, the expression “drivingly coupled” encompasses anarrangement in which the rotation of one element results in the rotationor movement of another element (e.g., directly or indirectly). Forexample, although rotor shaft 816 d does not directly touch shaft 104,the rotation of rotor shaft 816 d causes gear 818 d to rotate, whichengages the central gear 120 and causes shaft 104 to rotate. Forsimplicity, FIG. 9 depicts gear 818 c coupled to rotor shaft 816 c andgear 818 d coupled to rotor shaft 816 d. Reference numerals for othergears and rotor shafts have been omitted for simplicity. As depicted,rotors shafts 816 c, 816 d may have parallel rotational axes. In someembodiments, an additional gear 818 c′ may be connected to rotor shaft816 c. The use of additional gear 818 c′ may further reduce the stressand strain experienced by gears during operation, as the stress andstrain is distributed between two gears 818 c, 818 c′ rather thanconcentrated on a single gear. Example embodiments which incorporatemore than one gear are described in further detail below with referenceto FIG. 12.

In some embodiments, the windings 808 of first machine 810 may besupplied with electric power from a first single phase (phase A). Insome embodiments, the windings 108′ of second machine 810′ may besupplied with electric power from a second single phase (phase B). Insome embodiments, the windings 108″ of third machine 810″ may besupplied with electric power from a third single phase (phase C). PhaseB may be offset from phase A by 120 degrees. Phase C may be offset fromphase A by 240 degrees. As noted above, each machine 810, 810′, 810″includes a single common stator 822, 822′, 822″, respectively, and assuch each machine 810, 810′, 810″ is powered by a unique phase.

The output torque from each rotor shaft (e.g. 816 d) is equal to the sumof torques output by individual rotors (e.g. 802 d, 802 d′, 802 d″). Ifphase B is offset from phase A by 120 degrees, and phase C is offsetfrom phase A by 240 degrees, the net output torque provided by rotorshaft 816 d may have substantially less torque ripple relative to theoutput torque of any individual machine 810, 810′ or 810″. The outputtorque waveform may be similar in nature to that of FIG. 6 (although thequantitative torque output might not be similar between machines 400 and800). For example, if the output torque of rotor 802 d varies between 0and the maximum output torque, then the sum of the output torque ofrotor 802 d with rotors 802 d′ and 802 d″ (which are offset by 120degrees) would result in a far more stable output torque with lesstorque ripple than a single rotor.

Machine system 800 may also provide additional versatility andflexibility relative to other electric machines. For example, the samemagnetic circuit can be used for both high-input speed generators, aswell as low output speed propulsion motors by selecting the appropriateratio between the gears 818 and the central gear 120. The speedselection may be carried out without the addition of a separate gearbox,which avoids the costs and weight associated with a gearbox as would berequired by other electric machines.

Moreover, the machine 800 may allow for the use of the same bi-polerotors 802 in machines of different sizes, because any suitable numberof rotors 802 can be used to obtain the desired output torque. As such,cost savings may be achieved by using the same standardized rotors 802across different applications, rather than having to tailor rotors 802depending on the specific intended use of the machine 800. In addition,in machine 800, winding coils are exposed and the magnetic rotors 802are distributed around the machine assembly, which may facilitate heatextraction from the machine 800 in a more convenient manner relative tomachines where copper windings are contained within the stator iron.This may help to increase the power per weight and power per volumeratios of machine 800 relative to other electric machines.

FIG. 10A is a simplified schematic side cross-sectional view of anindividual rotor shaft 816 d of machine 800. As depicted, each rotorshaft 816 interconnects rotors 802 d, 802 d′, 802 d″ to gears 818 d, 818d′. FIG. 10B is a view of rotor 802 d on axis A-A in FIG. 10A. Asdepicted, rotor 802 d includes a magnet with north and south poles andan equator. FIG. 10C is a view of rotor 802 d′ on axis B-B in FIG. 10A.As depicted, rotor 802 d′ includes a magnet with north and south poles,and is mechanically indexed by 120 degrees relative to rotor 802 d. FIG.10D is a view of rotor 802 d″ on axis C-C in FIG. 10A. As depicted,rotor 802 d″ includes a magnet with north and south poles, and ismechanically indexed by 240 degrees relative to rotor 802 d, and by 120degrees relative to rotor 802 d′. It should be appreciated that althoughFIGS. 10A-10D illustrate a particular configuration of rotor indexing inmachine 800, it is contemplated that other configurations may be used inorder to enhance the operational characteristics of machine system 800.

In some embodiments, each rotor 802 in first machine 810 is connected toa respective rotor 802′ in second machine 810′ and a respective rotor802″ in third machine 810″ via a rotor shaft 816. In some embodiments,there may be fewer rotor shafts 816 than there are rotors in machine810.

FIG. 11 depicts an alternative configuration of an electric machinesystem 1100. Machine system 1100 is similar to machine system 800 inthat each machine 1110, 1110′, 1110″ contains a plurality of rotors anda single stator and phase for each machine. Machine system 1100 differsin that one winding 1108 is provided between every pair of rotors. Forexample, referring to FIG. 8, winding 808 ab may be provided betweenrotors 802 a and 802 b, and winding 808 cd may be provided betweenrotors 802 c and 802 d. However, every second winding (e.g. windings 808bc, 808 de, 808 fg, 808 hi, 808 jk, 808 lm) is omitted. Removing everysecond winding and rotating the middle machine 1110′ may allow for theinterlaced configuration depicted in FIG. 11.

As shown, the windings of each adjacent machine 1110, 1110′, 1110″ areoffset in such a manner that windings of adjacent machines cannot touch.This may provide an added benefit of reducing the possibility ofphase-to-phase short circuits, which may occur if windings from adjacentmachines are too closely packed together. As an additional advantage,the configuration of FIG. 11 may save axial space, which may beadvantageous in applications in which space is limited or at a premium.

It should be appreciated that although FIG. 9 depicts an embodiment ofmachine system 800 with machines 810 in 3 planes, it is contemplatedthat some embodiments may include fewer than 3 machines 810 in parallel,and some embodiments may include more than 3 machines 810 in parallel,connected via rotor shafts 816 to define common rotors between machines.

As noted above, in some embodiments, machine systems 400, 800, 1100 mayinclude more than one gear 418, 818 coupled to an individual rotor shaft416, 816. FIG. 12 is a partial cross-sectional view of an electricmachine system 1200 with multiple gears affixed or connected to eachrotor shaft 816. It should be noted that although machine 1200 isdescribed with reference to machine 800, the principles disclosed hereinrelating to machine 1200 with multiple gears per rotor shaft may beapplied to numerous electric machine systems (and in particular tomachine system 400 described herein).

As shown in FIG. 12, rotor shaft 816 d interconnects each of rotors 802d, 802 d′, 802 d″. Gear 818 d is connected to rotor shaft 816 d adjacentto rotor 802 d, and driving gear 818 d′ is connected to rotor shaft 816d adjacent to rotor 808 d″. Each of gears 818 d, 818 d′ is configured toengage with central gears. As depicted, driving gear 818 d engages witha first central gear 120, and driving gear 818 d′ engages with a secondcentral gear 120′. Each of central gears 120, 120′ are rotatably fixedto shaft 104. As such, when rotor shaft 816 d is caused to rotate byrotors 802 d, 802 d′, 802 d″, both of gears 818 d and 818 d′ are causedto drive central gears 120 and 120′, respectively. Thus, the net torqueapplied to central shaft 104 is the sum of the torque applied by gears818 d and 818 d′. It will be appreciated that relative to configurationswith only one gear 818 d per rotor shaft 816 d, roughly the same nettorque will be produced by the rotors 802 d, 802 d′, 802 d″. As such, ifgears 818 d, 818 d′ have the same dimensions and central gears 120, 120′have the same dimensions, the torque exerted by each gear 818 d, 818 d′would be expected to be roughly half of the torque applied by gear 818 din an embodiment with one gear (minus any additional losses caused bythe extra weight of the additional gear, and the like). Therefore, theaddition of second gear 818 d′ may result in the strain and stress oneach gear 818 d, 818 d′ being significantly reduced, which may allow forthe use of less expensive materials which are less resistant to stress(e.g. plastic), and may require less ongoing maintenance (e.g. lessoil).

Although FIG. 12 depicts two gears 818 d, 818 d′ per collective rotor,it should be appreciated that other embodiments which involve more thantwo gears (e.g. additional central gears and additional gears 818 dwhich are located between any of rotors 802 d, 802 d′, 802 d″) arecontemplated, and may further reduce the stress and strain experience bygears.

It should be further noted that although FIG. 12 depicts an embodimentin which both central gears 120 and 120′ are fixed to the same centralshaft 104, it is contemplated that in other embodiments, central gear120 may be fixed to a first input/output shaft 1304, and central gear120′ may be fixed to a second input/output shaft 1304′ which may rotateindependently from first input/output shaft 1304. As such, someembodiments of machine 1200 may be suitable for use in gearboxapplications, without requiring the addition of a gearbox to machine1200, which may provide numerous benefits relating to lower costs andreducing the weight and amounts of materials required for a givenapplication.

FIG. 13 is a schematic partial cross-sectional view of an electricmachine 1300 system having an independent input shaft 1304 and outputshaft 1304′. Machine system 1300 is similar to machine system 1200 inmany respects. Machine system 1300 includes one or more collectiverotors 1350 (for simplicity, only one collective rotor 1350 is shown).Rotor shaft 1316 interconnects rotors 1302, 1302′, 1302″ of machines1310, 1310′, 1310″ to define collective rotor 1350, and input gear 1318is fixed to an end of collective rotor 1350 adjacent to first rotor1302. Output gear 1318′ is fixed to another end of collective rotor 1350adjacent to third rotor 1302″. In some embodiments, collective rotors1350 have parallel rotational axes. In some embodiments, the collectiverotors 1350 may be disposed to define a circular array arrangement.Although FIG. 13 depicts machine 1300 having 3 rotors per collectiverotor, it will be appreciated that embodiments with as few as oneelectric machine rotor per collective rotor 1350 are contemplated.Embodiments with more than 3 electric machine rotors per collectiverotor 1350 are also contemplated. In some embodiments, the electricmachine rotors are axially spaced apart between the input gear 1318 andoutput gear 1318′.

As depicted, input gear 1318 is drivingly coupled to input shaft 1304via first central gear 1320. First central gear may be fixed to inputshaft 1304. Output gear 1318′ is drivingly coupled to output shaft 1304′via second central gear 1320′. Second central gear 1320′ is coupled tooutput shaft 1304′. In some embodiments, input shaft 1304 is connectedto a gas turbine. In some embodiments, output shaft 1304′ is connectedto a propeller or fan. It will be appreciated that the speed at whichinput shaft rotates may be substantially different (faster or slower)from the speed at which output shaft rotates. Normally, a separategearbox may be used to transfer mechanical energy from one rotating gearto another. However, in the embodiment shown in FIG. 13, no separategearbox is required.

Instead, the sizes of first central gear 1320, input gear 1318, outputgear 1318′ and second central gear 1320′ may be chosen such that thegear ratios allow for a rotation at the input shaft 1304 to result in arotation in or around a desired speed at output shaft 1304′. Suchrotation is achieved by the rotation of input shaft 1304 causing firstcentral gear 1320 to rotate. The rotation of first central gear 1320causes input gear 1318 to rotate at an angular speed. Output gear 1318′shares rotor shaft 1316 with input gear 1318, and so the output gear1318′ will also rotate at the same angular speed as input gear 1318.Output gear 1318′ is coupled to second central gear 1320′, and so therotation of output gear 1318′ causes the rotation of second central gear1320′, thereby causing the resulting rotation of output shaft 1304′.

In some embodiments, electrical rotors 1302, 1302′, 1302″ in machinesystem 1300 are operable in a generating mode and in a motoring mode.When electrical rotors 1302, 1302′, 1302″ are operating in a motoringmode, the rotor shafts 1316 may be indexed to provide a torque phaseoffset relative to each other. When electrically powered, the mechanicalpower at the input shaft 1304 is transmitted through machine 1300 in amanner similar to that of a gearbox. When electrical rotors 1302, 1302′,1302″ are electrically powered, the power output to output shaft 1304′is the sum of the mechanical power at input shaft 1304 and the outputpower of machines 1310, 1310′, 1310″. As such, in situations where themechanical input power at shaft 1304 is insufficient to achieve thedesired output at output shaft 1304′, machines 1310, 1310′, 1310″ may beelectrically powered so as to provide additional output power to outputshaft 1304′.

In addition, the machine system 1300 can act as an in-line generator toconvert some of the mechanical input power at shaft 1304 to electricalcurrent at windings 1308, 1308′, 1308″. This electrical power may beused for various purposes, such as, for example, aircraft electricalsystems, charging batteries, or the like. In some embodiments (e.g.turbine engines), the generated electrical power may be used toaccelerate or apply positive torque to the high pressure spool orcompressor spool of an engine core.

Contrary to conventional hybrid electrical applications, the assistanceprovided by machine 1300 is not applied on a high-speed output shaft orto an auxiliary pad of a reduction gearbox. Instead, machine 1300 mayact as a gearbox with an electric machine embedded therein.

Of course, the above described embodiments are intended to beillustrative only and in no way limiting. The described embodiments aresusceptible to many modifications of form, arrangement of parts, detailsand order of operation. The invention is intended to encompass all suchmodification within its scope, as defined by the claims.

What is claimed is:
 1. An electric machine system comprising: a firstelectric machine configured to drive a load, the first electric machinehaving a plurality of first rotors; a second electric machine having aplurality of second rotors, at least one of the second rotors indexedrelative to a respective one of the first rotors to, in use, provide atorque phase offset between the first and second electric machines; andtwo or more shafts coupled to the load, each shaft of said two or moreshafts interconnecting a respective one of the first rotors with arespective one of the second rotors, the respective one of the firstrotors being coaxial with and axially spaced apart from the respectiveone of the second rotors, said two or more shafts being nonconcentric;wherein: the first rotors are disposed to define a first circular arrayarrangement; and the second rotors are disposed to define a secondcircular array arrangement.
 2. The electric machine system of claim 1,further comprising a third electric machine having a plurality of thirdrotors, at least one of the third rotors indexed relative to therespective one of the first rotors and the at least one of the secondrotors to, in use, provide a torque phase offset between the first andthird electric machines and a torque phase offset between the second andthird electric machines, wherein the at least one of the third rotors isconnected to one of the two or more shafts.
 3. The electric machinesystem of claim 1, wherein the torque phase offset between the firstelectric machine and the second electric machine is 120 degrees.
 4. Theelectric machine system of claim 2, wherein the torque phase offsetbetween the second electric machine and the third electric machine is120 degrees.
 5. The electric machine system of claim 2, wherein arespective one of the rotors in the pluralities of first, second andthird rotors are disposed at different axial positions relative to theone of the two or more shafts.
 6. The electric machine system of claim2, wherein a respective one of the rotors in the pluralities of first,second and third rotors are coaxial.
 7. The electric machine system ofclaim 1, wherein the two or more shafts are drivingly coupled to theload via one or more gears.
 8. The electric machine system of claim 1,wherein a respective one of the rotors in the pluralities of first andsecond rotors are disposed at different axial positions relative to oneof the two or more shafts.
 9. The electric machine system of claim 1,wherein adjacent first rotors are indexed to have a positional phaseoffset of 180 degrees with each other.
 10. The electric machine systemof claim 1, wherein adjacent second rotors are indexed to have apositional phase offset of 180 degrees with each other.
 11. The electricmachine system of claim 1, wherein the two or more shafts are drivinglycoupled to the load via respective gears.
 12. The electric machinesystem of claim 1, wherein the two or more shafts have parallel rotationaxes.
 13. The electric machine system of claim 1, wherein the firstcircular array arrangement of first rotors is coaxial with the secondcircular array arrangement of second rotors.
 14. The electric machinesystem of claim 1, wherein the first circular array arrangement of firstrotors is axially offset from the second circular array arrangement ofsecond rotors.
 15. An electric machine system comprising: a firstelectric machine configured to drive a load, the first electric machinehaving a plurality of first rotors; a second electric machine having aplurality of second rotors, at least one of the second rotors indexedrelative to a respective one of the first rotors to, in use, provide atorque phase offset between the first and second electric machines; twoor more shafts coupled to the load, each shaft of said two or moreshafts interconnecting a respective one of the first rotors with arespective one of the second rotors, the respective one of the firstrotors being coaxial with and axially spaced apart from the respectiveone of the second rotors, said two or more shafts being nonconcentric;and a third electric machine having a plurality of third rotors, atleast one of the third rotors indexed relative to the respective one ofthe first rotors and the at least one of the second rotors to, in use,provide a torque phase offset between the first and third electricmachines and a torque phase offset between the second and third electricmachines, wherein the at least one of the third rotors is connected toone of the two or more shafts.
 16. The electric machine system of claim15, wherein the torque phase offset between the second electric machineand the third electric machine is 120 degrees.
 17. The electric machinesystem of claim 15, wherein a respective one of the rotors in thepluralities of first, second and third rotors are disposed at differentaxial positions relative to the one of the two or more shafts.
 18. Theelectric machine system of claim 15, wherein a respective one of therotors in the pluralities of first, second and third rotors are coaxial.